Modify a regular door stop and added magnets, this allows the door to be held open by the magnets. The magnets are Neodymium Rare Earth Magnet, the dimensions are 10mm diameter and 5mm tall.

Plan A
a) For the magnets Google or eBay search "Disc Magnets N35 10mm 5mm 3mm"
b) When installing the door magnet remember that they have to be in opposite polarities for the magnets to attract each other, otherwise they will repel each other.

Plan B
Instead of using two magnets, one side can just be a set of metal washers google search "Metal Steel Washer 10mm x 3mm"